In recent years, photographic film cartridges have been proposed in which the film strip is completely enclosed within the cartridge and the film is loaded into the camera by simply causing the cartridge film spool to be rotated in the unwinding direction. A motor drive in the camera would generally be used for this purpose. Simplicity in film loading is one reason for this arrangement.
A problem with this arrangement, however, is that, unlike prior conventional film cartridges, there is no film leader extending out of the cartridge to indicate that the film is unexposed. Consequently, arrangements have been proposed to provide a visual indication of the exposure condition of the film and also to prevent loading of exposed film into the camera. This is particularly useful if the photographer wishes to switch cartridges to a different film type midway through the film exposures in the first cartridge. Commonly assigned U.S. Pat. No. 4,994,833 and the applications cross-referenced therein are representative of such proposals. However, such arrangements have the drawback that they require specially designed cartridge configurations and special mechanical sensors built into the camera to implement the double exposure prevention.
In commonly assigned U.S. Pat. Nos. 5,030,978 and 5,032,854, film cartridges are disclosed that utilize a rotatable radial bar coded disc element to provide information about the film in the cartridge, such as film manufacturer, film type, etc.. These patents describe apparatus and methods for reading the bar codes during rewind operation to position the spool and the associated bar coded disc at a particular angular position of the spool so as to align visual indicators on the cartridge that indicate the exposure condition of the film, e.g. unexposed, partially exposed or exposed. In the '854 patent, a simple locking feature is shown that holds the spool in the desired indicator position. While useful as a visual indicator of film exposure condition, no provision is made for enabling the camera to automatically prevent reloading of exposed film or of enabling reloading of partially exposed film to an available frame position without the use of the special cartridge configuration and mechanical sensors of the types considered in aforementioned U.S. Pat. No. 4,994,833.
It is therefore considered desirable to provide camera apparatus that will cooperate with a film cartridge having a radial coded disc arrangement and that will conveniently and reliably prevent double exposure of film in the cartridge without the need for a specially designed film cartridges and costly, space consuming mechanical sensor arrangements in the camera.